[Qemu-devel] [PATCH] hw/i386: add device tree support

[Antonio Borneo <borneo.antonio@gmail.com>]

With "-dtb" on command-line:
- append the device tree blob to the kernel image;
- pass the blob's pointer to the kernel through setup_data, as
  requested by upstream kernel commit da6b737b9ab7 ("x86: Add
  device tree support").

The device tree blob is passed as-is to the guest; none of its
fields is modified nor updated. This is not an issue; the kernel
commit above uses the device tree only as an extension to the
traditional kernel configuration.

To: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
To: Richard Henderson <rth@twiddle.net>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: qemu-devel@nongnu.org
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
---

Hi,

I'm not expert on the x86 memory map at boot and during kernel
boot; I found easy to just append the dtb to the kernel image.
>From my tests this patch is working fine.
If you have any hint for a different loading address for dtb, I
would be glad to modify this code.

Regards,
Antonio

 hw/i386/pc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 2ac97c4..d928b90 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -813,11 +813,26 @@ static long get_file_size(FILE *f)
     return size;
 }
 
+/* setup_data types */
+#define SETUP_NONE     0
+#define SETUP_E820_EXT 1
+#define SETUP_DTB      2
+#define SETUP_PCI      3
+#define SETUP_EFI      4
+
+struct setup_data {
+    uint64_t next;
+    uint32_t type;
+    uint32_t len;
+    uint8_t data[0];
+} __attribute__((packed));
+
 static void load_linux(PCMachineState *pcms,
                        FWCfgState *fw_cfg)
 {
     uint16_t protocol;
     int setup_size, kernel_size, initrd_size = 0, cmdline_size;
+    int dtb_size, setup_data_offset;
     uint32_t initrd_max;
     uint8_t header[8192], *setup, *kernel, *initrd_data;
     hwaddr real_addr, prot_addr, cmdline_addr, initrd_addr = 0;
@@ -825,8 +840,10 @@ static void load_linux(PCMachineState *pcms,
     char *vmode;
     MachineState *machine = MACHINE(pcms);
     PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
+    struct setup_data *setup_data;
     const char *kernel_filename = machine->kernel_filename;
     const char *initrd_filename = machine->initrd_filename;
+    const char *dtb_filename = machine->dtb;
     const char *kernel_cmdline = machine->kernel_cmdline;
 
     /* Align to 16 bytes as a paranoia measure */
@@ -989,6 +1006,35 @@ static void load_linux(PCMachineState *pcms,
         exit(1);
     }
     fclose(f);
+
+    /* append dtb to kernel */
+    if (dtb_filename) {
+        if (protocol < 0x209) {
+            fprintf(stderr, "qemu: Linux kernel too old to load a dtb\n");
+            exit(1);
+        }
+
+        dtb_size = get_image_size(dtb_filename);
+        if (dtb_size <= 0) {
+            fprintf(stderr, "qemu: error reading dtb %s: %s\n",
+                    dtb_filename, strerror(errno));
+            exit(1);
+        }
+
+        setup_data_offset = QEMU_ALIGN_UP(kernel_size, 16);
+        kernel_size = setup_data_offset + sizeof(struct setup_data) + dtb_size;
+        kernel = g_realloc(kernel, kernel_size);
+
+        stq_p(header+0x250, prot_addr + setup_data_offset);
+
+        setup_data = (struct setup_data *)(kernel + setup_data_offset);
+        setup_data->next = 0;
+        setup_data->type = cpu_to_le32(SETUP_DTB);
+        setup_data->len = cpu_to_le32(dtb_size);
+
+        load_image(dtb_filename, setup_data->data);
+    }
+
     memcpy(setup, header, MIN(sizeof(header), setup_size));
 
     fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, prot_addr);
-- 
2.8.0